1. Field of the Invention
This invention relates to water-free detergent mixtures containing long-chain and relatively short-chain alkyl sulfates in selected mixing ratios and hydrophobic structure breakers and to the use of these mixtures for the production of solid detergents.
Anionic surfactants, more particularly alkyl sulfates or fatty alcohol sulfates, are important constituents of laundry detergents, dishwashing detergents and cleaning formulations. In contrast to nonionic surfactants, which exhibit inverse solubility behavior and which, by virtue of hydrogen bridge bonds, show better solubility in cold water than in warm water, anionic surfactants show conventional behavior, i.e. their solubility increases more or less linearly with the temperature until the solubility product is reached. However, for technical applications, for example with regard to dispensing behavior during the washing process, there is a need for anionic surfactants which show adequate solubility even in cold water.
In the past, there has been no shortage of attempts to improve the problem posed by the inadequate solubility of anionic surfactants, more particularly alkyl benzene sulfonates, fatty alcohol sulfates and .alpha.-methyl ester sulfonates, in cold water. These attempts have mostly been based on two concepts, namely:
a) the use of hydrotropes and PA1 b) surface enlargement of the surfactant particles.
Short-chain alkylaryl sulfonates, for example toluene, xylene or cumene sulfonate, are undoubtedly among the most well-known hydrotropes. They are suitable, for example, as solubilizers for anionic and nonionic surfactants in the production of liquid detergents. The improvement in solubility is probably attributable to advantageous mixed micelle formation, cf. the review by H. Stache in Fette, Seifen, Anstrichmittel 71, 381 (1969). However, the improvement in cold water solubility, especially in the case of fatty alcohol sulfates, is normally achieved by adding surfactants with high HLB values, for example highly ethoxylated polyglycol ethers (tallow alcohol.multidot.40 EO adduct) or the like, to them as hydrotropes. Unfortunately, the dissolving rates obtainable in this way, especially in the case of fatty alcohol sulfates, are unsatisfactory for a number of technical applications.
2. Discussion of Related Art
According to the teaching of DE-A-41 24 701 (Henkel), solid detergents of high apparent density and improved solubility are obtained by adding polyethylene glycol ethers with molecular weights in the range from 200 to 12,000 and preferably in the range from 200 to 600 to mixtures of anionic and nonionic surfactants and then drying the resulting mixtures and/or converting them into solid form. Example 1 discloses a detergent formulation containing C.sub.12-18 fatty alcohol sulfate, C.sub.12-18 fatty alcohol.multidot.5 EO and C.sub.16-18 tallow fatty alcohol.multidot.5 EO adduct and - based on the nonionic surfactants - not less than 45% by weight of polyethylene glycol with a molecular weight of around 400 which is extruded and granulated after homogenization. However, the dissolving rate of the solid detergents obtained is not always satisfactory. In addition, the presence of the large quantities of polymer required is undesirable.
EP-A-0 208 534 relates generally to spray-dried detergent compositions which, in addition to anionic surfactants, contain nonionic surfactants, polyacrylates and polyethylene glycol ethers with an average molecular weight in the range from 1,000 to 20,000. According to the teaching of this document, the dispersibility of anionic surfactants can be improved by adding nonionic surfactants, polyethylene glycol ethers (PEG) and polyacrylates to them. The only Example describes a mixture containing alkyl benzene sulfonate and fatty alcohol sulfate to which a C.sub.12-13 oxoalcohol.multidot.6.5 EO adduct, sodium polyacrylate and polyethylene glycol with a molecular weight of around 8,000 are added. The ratio by weight of nonionic surfactant to PEG is 1:1.
DE-A-21 24 526 relates to foam-regulated detergents and cleaning compositions. Example 6 discloses compositions containing tallow alcohol sulfate, alkyl benzene sulfonate and polyethylene glycol with a molecular weight of around 20,000.
Other process developments concerning the production of solid anionic surfactants are merely mentioned in passing at this juncture. For example, solid detergents obtained by treating water-containing alkyl sulfate pastes with soda and zeolites and then extruding the pastes are known from International patent application WO-A-92/09676 (Henkel). The dissolving rate of the solids is not discussed in this document.
International patent application WO-A-91/02047 describes a process for the production of high-density washing- or cleaning-active extrudates in which a solid free-flowing compound containing a plasticizer and/or lubricant is extruded under pressure to form strands and, after leaving the multiple-bore extrusion die, the strands are cut to the predetermined granule size by means of a cutting unit. Full particulars of the extrusion process can be found in International patent applications WO-A-93/02176 and WO-A-94/09111. In one preferred embodiment of the invention, the compound is preferably delivered continuously to a twin-screw extruder with co-rotating or contra-rotating screws, of which the housing and the extruder/granulation head can be heated to the predetermined extrusion temperature. Under the shearing effect of the screws, the compound is compressed under pressure (preferably under a pressure of at least 25 bar or, where the throughputs are extremely high, under an even lower pressure, depending on the machine used), plasticized, extruded in the form of strands through the multiple-bore extrusion die in the extrusion head and, finally, the extrudate is size-reduced by a rotating cutting blade, preferably to substantially spherical or cylindrical granules. The bore diameter of the multiple-bore extrusion die and the length to which the strands are cut are adapted to the dimensions selected for the granules. In this embodiment, it is possible to produce granules with a particle size determined substantially uniformly in advance, the absolute particle sizes being adaptable to the application envisaged. Particle diameters of up to at most 0.8 cm are preferred. Important embodiments are aimed at the production of uniform granules in the millimeter range, for example in the range from 0.5 to 5 mm and, more particularly, in the range from about 0.8 to 3 mm. In one important embodiment, the length-to-diameter ratio of the primary granules formed is in the range from about 1:1 to about 3:1. In another preferred embodiment, the still plastic and moist primary granules are subjected to another shaping step in which any edges present in the crude extrudate are rounded off so that spherical to substantially spherical extrudates are ultimately obtained. If desired, small quantities of a dry powder, for example zeolite powders, such as zeolite NaA powder, may be applied in this stage. This shaping step may be carried out in conventional spheronizing machines. It is important to ensure that only small quantities of fine particles are formed in this stage. The extrudates are then preferably subjected to a drying step, for example in a fluidized bed dryer. The extruded granules, which may also contain peroxy bleaching agents, for example perborate monohydrate, may be dried without any loss of active oxygen at feed air temperatures of 80.degree. to 150.degree. C. Alternatively, it is even possible to carry out the drying step immediately after extrusion of the crude extrudate and hence before any optional final shaping step in a spheronizer. The extrudates may then be blended with other constituents of detergents or cleaning formulations.
Now, the problem addressed by the present invention was to make alkyl sulfates available in such a form that, after mixing with other detergent ingredients and mechanical compaction, they would give detergents or cleaning formulations which would be readily soluble even in cold water and of which the production would be free from the disadvantages mentioned above.